3 phase stacking GSLC's

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JasonPAtkins
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3 phase stacking GSLC's

Post by JasonPAtkins » Wed Sep 11, 2019 1:33 pm

Hi all, this is the third 10kw+ off-grid system I've been involved with, but the first using Radian inverters. I'll be using 3 x GS7048e's to generate 3ph 400v 50hz power for a non-profit in West Africa.

I'm sure I'll have more questions, but I'm currently spec'ing and ordering. I'm ordering the GSLC's for the three inverters, despite realizing the installation manual advises against stacking more than 2 inverters in GSLC's because of wiring complexity, because I'm going to take care of all of the AC distribution external to the GSLC's, so there should be plenty of room in the GSLC's for the DC stuff.

Actually, my question would be the same even if I were just stacking two units - so ignore the above, haha...

My question is, what's the official way to tie the DC buses of separate GSLC's together? In other words, I don't want to run battery connections to/from each GSLC, so the DC+ and DC- busses need to be tied together. I'll mount the units close with a big horizontal conduit connection between the GSLC's, so would you just run a 2' length of 4/0 from one to the next? I want to install the flexnet dc monitor that uses the shunt, so I assume that would have to happen in only one spot - cause if current is passing through one of the other negative busses and over that shunt, it won't get counted.

So I'm envisioning the battery connections coming into one GSLC (let's call it the main), and it'll be the main where the dc monitor is installed. Then, on the other (non-battery) side of the shunt of the "main" GSLC's dc- bus, I can make connections to the other GSLC's dc-'s, and similarly tie all three DC+ cable plates together with fat cables. That will give me solar controllers plus inverters tying into the now-common dc busses, but all of the current going to or from the batteries all going through the single shunt, letting the dc monitor correctly meter.

Does this seem like the best way to do it, or is there a better/easier way?

kayak1
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My RE system: 77xRec 315 Watt Panels
GS8048A Inverter, 2xFM100 Charge Controller, Mate3S, Flexnet DC, 12xEnergyCell PLR 600 AH AGM. (Attached with Tigo Otimizers to 38 panels)
Solar Edge 10KW inverter Attached with Solar Edge Optimizers to 41 panels.

Re: 3 phase stacking GSLC's

Post by kayak1 » Thu Sep 12, 2019 7:03 am

Have you looked at the midnight solar Battery Combiner, it has a version with the correct shunts built into it, to allow you to use the flexnet dc.
-Jason

EMCF
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Re: 3 phase stacking GSLC's

Post by EMCF » Thu Sep 12, 2019 4:52 pm

The safe and official way to connect the DC busses is, from battery bank, run one separate positive cable in series with a breaker to each GSLC. Yes, your negative can be common, and without a breaker. Run one cable to "phase A" GSLC, then make jumper cable to "phase B" GSLC, and another jumper cable to "phase C" GSLC.
This configuration will enable you to power down one or two of the inverters, and can still have a 230VAC output. If you power down one, you can still have a 400VAC output.

JasonPAtkins
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Re: 3 phase stacking GSLC's

Post by JasonPAtkins » Fri Nov 08, 2019 1:11 pm

Thanks for the answers.

EMCF, your illustration touches on one of my biggest irritations with Outback hardware (only beating the MATE's UI and menuing system). The ability to do what you just described, supplying two phases of a three phase stack, is incredibly dangerous to connected 3ph equipment, and in my opinion, should almost never be done - but should DEFINITELY not be the only option, or even the default option, for handling the condition where one inverter of a 3ph stack goes down. Xantrex XW's handle the situation correctly - if one of the inverters has an error that causes its output to drop out while part of a three phase stack, both of the other inverters shut down as well. You could fry an entire workshop's worth of 3 phase motors in about 15 seconds if you didn't have external phase protection installed. I have installed a phase protector that opens a contactor feeding my entire shop if it detects such a condition, but shouldn't need to do that - the inverters should (at the very least be able to be configured to) all cut output together if one goes down. This is obviously a different story where you have two or three inverters operating in parallel, where if one goes down you want the other two to take up the slack and continue powering the load.

Anyway, that complaint aside, I don't need the ability to do what you're describing, so I would like to have a common positive bus (among the GSLC's) as well, but want to do it in a way that will run all of the current through one GSLC's shunt so the flexnet can still tie in there. The only problem I foresee is the current limitation of the shunt - does anyone know what it is? In other words, what I'd like to do is connect the battery positive to one side of one of the GSLC's shunts, and then come off of the other side of that same shunt to tie into the DC+ of the other two GSLC's.

Kayak1 - are you saying the Midnite product has a shunt, or has a shunt that can handle 3 inverter's worth of DC current? These GSLC's have the shunt, I believe, I'm just not sure it's appropriate for the case I'm describing. I know the manual advocates a different solution if stacking more than two inverters, but in my case, if this shunt issue isn't an issue, there will be enough space to make all of the connections, because I'm not going to handle any of the AC stuff inside these boxes, those three legs will get pulled out to a disconnect and then off to AC distr panels.

Second question - does anyone know how much space is between Radian inverters when mounted per the instructions? I ask because I plan to use the 2" knockouts in the GSLC's to run cables between them - but if the GSLC's are touching, I'll just need a plastic knockout protector to keep cables from getting cut on the metal of the case. If there's some gap, I assume I'll need a conduit nipple to bridge the gap.

JasonPAtkins
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Re: 3 phase stacking GSLC's

Post by JasonPAtkins » Fri Nov 08, 2019 3:05 pm

Hmmm... it appears that Outback had already anticipated my need? The docs for the FN-DC say it can monitor up to three different shunts at once. So if that's the case, I can tie the three DC+ buses together, run separate from BATT- into each of the three shunts, and in this way still monitor them all (assuming the FN-DC can sum the three shunts to get total system draw?), while not running all of the current through just one shunt!

https://d1819pwkf4ncw.cloudfront.net/fi ... -44031.pdf

EMCF
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Re: 3 phase stacking GSLC's

Post by EMCF » Fri Nov 08, 2019 4:35 pm

Jason, this is a reply to your 1:11 pm post.
I may have not described my DC connections very clear. The negative and positive bus are actually both have common connections, with the difference that the battery breakers are in the positive cables. The basic GSLC usually comes with 2 shunts, one for CC, and one for inverter. These shunts can carry DC amps up to 500ADC, so a single shunt can carry the DC current of all 3 inverters combined. Attached is my handwritten diagram on how I can wire your system using a single shunt.



On another note, there is actually a use case for a three phase power supplying two inverters configured as three phase. Here in North America, in some industrial buildings there are cases where the service connection is 120/120/208. This means these are L1-N-L2 of a three-phase distribution system. For 2 Outback FXR 120v output inverters configured for 3-phase, those are exactly the input that is needed.
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kayak1
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My RE system: 77xRec 315 Watt Panels
GS8048A Inverter, 2xFM100 Charge Controller, Mate3S, Flexnet DC, 12xEnergyCell PLR 600 AH AGM. (Attached with Tigo Otimizers to 38 panels)
Solar Edge 10KW inverter Attached with Solar Edge Optimizers to 41 panels.

Re: 3 phase stacking GSLC's

Post by kayak1 » Sat Nov 09, 2019 2:52 am

As I can't post links in replies and have them not be deleted please google:
"MIDNITE SOLAR 1000ADC MAX 1000A/100MV SHUNT BATTERY COMBINER"

Go to the midnight solar link not one of the amazon ones and you can see the base box.

They have an option positive and optional breakers you can install in it.

With outback you can install larger shunts but the ADC MV ratio needs to be maintained.

JasonPAtkins
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Re: 3 phase stacking GSLC's

Post by JasonPAtkins » Thu Nov 14, 2019 12:36 pm

EMCF wrote:
Fri Nov 08, 2019 4:35 pm
Jason, this is a reply to your 1:11 pm post.
I may have not described my DC connections very clear. The negative and positive bus are actually both have common connections, with the difference that the battery breakers are in the positive cables. The basic GSLC usually comes with 2 shunts, one for CC, and one for inverter. These shunts can carry DC amps up to 500ADC, so a single shunt can carry the DC current of all 3 inverters combined. Attached is my handwritten diagram on how I can wire your system using a single shunt.



On another note, there is actually a use case for a three phase power supplying two inverters configured as three phase. Here in North America, in some industrial buildings there are cases where the service connection is 120/120/208. This means these are L1-N-L2 of a three-phase distribution system. For 2 Outback FXR 120v output inverters configured for 3-phase, those are exactly the input that is needed.
Thanks for the diagram - that's pretty similar to what I was imagining.

Last I heard, the 110v versions of the vfx (I think) and Radian (I'm pretty sure) can't be configured in a three phase stack, so if that's true then your case isn't supported anyway. Either way, "keep supplying partial 3 phase power" should DEFINITELY not be the only way, and shouldn't even be the default. If 110v inverters can 3ph stack, and your use case is a supported one, then there should be a "Keep supplying if other phases drop out" setting, and it should default to off, so that your use case can turn it on.

EMCF
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Re: 3 phase stacking GSLC's

Post by EMCF » Thu Nov 14, 2019 1:20 pm

JasonPAtkins wrote:
Thu Nov 14, 2019 12:36 pm
Last I heard, the 110v versions of the vfx (I think) and Radian (I'm pretty sure) can't be configured in a three phase stack, so if that's true then your case isn't supported anyway. Either way, "keep supplying partial 3 phase power" should DEFINITELY not be the only way, and shouldn't even be the default. If 110v inverters can 3ph stack, and your use case is a supported one, then there should be a "Keep supplying if other phases drop out" setting, and it should default to off, so that your use case can turn it on.
1. Outback's designed for North America inverters have rated output of 120VAC not 110VAC
2. The successor to VFX types, the FXR types inverters can be configured for three phase, that is a fact, not my opinion.
3. Radian E types can be configured for 3 phase, as what you are planning. Of course, the Radian A, being split phase, 120/120/240, can't be configured for 3 phase
4. If you read the VFXR manual, there is such a thing called "Multi-Phase Coordination". Here, if the master or sub-phase master inverter do not sense an acceptable AC source, the entire system disconnects from the source. None of the inverters will reconnect until the source is acceptable. You can disable it too. Does that take care of your "keep supplying..." concern?

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